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Signal processing
BY GISLE BJØNTEGÅRD
Introduction
Signal processing has a large number of applications. In this
presentation we will focus on image compression. The new
compression techniques have made it possible to fit live video
into networks originally intended for other purposes – speech or
data transmission with low capacity. In this context the following
applications are studied and achievements will be reported
in more detail below:
- Compress live video with “video phone quality” to fit into a
modem used on an analogue telephone line
- Compress live video with “teleconferencing quality” to fit
into basic access ISDN (2B)
- Compress live video with “at least VHS quality” to fit into a
2 Mb/s channel
- Compress live video with “TV quality” to fit into a 4 Mb/s
channel.
The development of compression techniques have largely been
undertaken by standardisation bodies like ITU and ISO. NTR
has actively taken part in the development related to all the
applications mentioned above.
This summary presents the outcome and status of the work in
the following research and standardisation organisations:
- European Co-operation in the Fields of Scientific and Technical
Research (COST)
- International Standardization's Organization (ISO)
- International Telecommunication Union Standardisation Sector
(ITU-T)
- European Telecommunication Standards Institute (ETSI).
Table 1 Main standards in the area of video compression
Name Organisation ID Applications
JPEG ISO IS-10918 Compression of still pictures
H.120 CCITT H.120 Video conferencing. 2 Mbps
H.261 CCITT H.261 Video telephony, Video
conferencing. 64–2000 Kbps
MPEG1 ISO IS-11172 Video storage. 1.5 Mbps
MPEG2 ISO IS-13818 Digital TV
H.262 ITU-T H.262 TV quality video on ATM
networks
COST
The COST 211 project (continued through COST 211bis and
COST 211ter) has played an important role in developing the
techniques used in all relevant standards today. In the following
we have summarised some important achievements made by
COST.
- The H.120 standard from the early eighties was completely
developed in COST 211.
- The H.261 standard for video conferencing was largely based
on inputs from COST 211bis.
- ISO/MPEG1 standard (see below) uses the same basic elements
as H.261.
- COST 211ter made significant contributions to ISO/MPEG2.
- The ongoing development of the ITU-T very low bitrate
video phone standard will use the model developed by COST
211ter as a basis for their work. The main job of developing
this model is done by NTR.
- For the coming ISO/MPEG4 standard (see below) the proposal
based on another COST model is expected to be an
important input.
NTR had the chairmanship of the simulation group in COST
211ter during the last two years – which turned out to be a very
important period for preparing methods for new video compression
standards.
ITU-T
The H.261 standard was developed in CCITT/SGXV Working
party XV/1. It was finalised in 1990 and is intended for bitrates
p*64 kbit/s. p=1,30. The main participants in this development
were national telecom operators. The chairman of the experts
group was Mr. Sakae Okubo from NTT, Japan.
In 1991 CCITT/SGXV Working party XV/1 initiated a new
experts group with the same chairman and with the mandate to
develop a video compression method for ATM (Asynchronous
Transfer Mode) networks. From the beginning it was decided to
do this development in co-operation with ISO/MPEG. The
meetings have been combined and CCITT/SGXV – now ITU-T
SG15 – have decided that the resulting standard shall have common
text with the ISO/MPEG2 standard. The contributions
from ITU in this combined work have largely been focusing on
issues of special interest for real time communications like coding/decoding
delay and handling of the type of packet loss that
may occur in ATM networks. The resulting standard is intended
for full TV quality and bitrates of a few Mb/s (typically 2 –
8 Mb/s).
The standard will be called H.262 and will be finished late
1994.
In 1993 ITU-T SG15 initiated an experts group on low bitrate
video phone. The scope of this group is to make standards for
complete video phones to operate on modems over analogue
telephone lines. The work will cover video compression, audio